(a) Field of the Invention
An exemplary embodiment of the present invention relates to a fuel cell system. More particularly, the present invention relates to a fuel cell system and an operating method thereof that improves performance of a fuel cell stack.
(b) Description of the Related Art
A fuel cell system is a kind of electrical generation system converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Typically, hydrogen is the most common fuel, but hydrocarbons such as natural gas and alcohols like methanol are sometimes used as alternative fuels.
A fuel cell system typically includes a stack which includes a plurality of individual fuel cells forming an electrical generation assembly, each having a cathode and an anode that allow charges to move between the two sides of the fuel cell. The fuel cell system also includes an air supply device for supplying the cathode of the fuel cell with air, and a hydrogen supply device for supplying the anode of the fuel cell with hydrogen. Here, high temperature and humid air can be exhausted from the cathode of a fuel cell, and high temperature and dry air can be exhausted therefrom during a high power operation. Further, no reacted hydrogen having moisture should be exhausted from the anode of the fuel cell.
Also, the fuel cell system includes a humidifier that humidifies air that is supplied from the air supply device with the air that is exhausted from the cathode of the fuel cell. Accordingly, the humidifier humidifies the air supplied from the air supply device with the air exhausted from the cathode of the fuel cell to supply the humidified air to the cathode.
However, conventionally, the supply air is humidified by the air that is exhausted from the cathode of the fuel cell through a membrane and the humidified air is then supplied to the cathode, and therefore the humidification effect of the fuel cell may in some instances be insufficient.
Furthermore, another problem with conventional fuel cell systems is that when the fuel cell system is started, the fuel cell system accelerates the degradation of a catalyst layer by an OCV (open circuit voltage) which decreases the durability of the system. As a solution to this problem, when the system is started, a separate hydrogen purge device is used to purge the fuel cell with hydrogen. However, the addition of a purge system, not only makes the system complicated but expensive as well.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.